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REVIEW Open Access
Applications of sand roasting and baking inthe preparation of
traditional Indian snacks:nutritional and antioxidant statusAruna
Jyothi Kora1,2
Abstract
Background: In India, the sand roasting technique is widely used
by street food vendors, villagers and cottageindustries for making
various value-added food products from different cereals, millets
and legumes. Thetraditionally produced sand-roasted products are
commonly utilized as ready to eat snacks or for the preparation
ofvarious other snacks.
Results: During the high-temperature short-time treatment of
sand roasting, the produced products are bestowedwith
characteristics such as higher puffing, crispiness, volume, and
improved color, aroma, flavor and texture. Interms of nutrition,
the roasting process enhances the carbohydrate and protein
digestibility, β-glucan extractability,levels of dietary fiber,
minerals, and antioxidants and reduces the inherent antinutrients
levels in cereals andlegumes. In addition, the complete destruction
of seed microflora enhances the shelf life and thus
consumeracceptance. The sand-roasted products act as prebiotic
dietary fiber and serves as an alternative to polished grainsfor
the consumers. Thus, the simplest, inexpensive, traditional sand
roasting method of dry heat application is usedfor making precooked
ready to eat weaning foods and preparation of cost-effective
dietary pediatric and geriatricformulations. The technique is also
employed for roasting various beans, fryums, nut, and pulse
decortication andas a pretreatment process for tamarind kernel
powder production, while the sand baking method is widely used
forbaking cakes, vegetables, meat, fish, eggs and starchy
tubers.
Conclusions: The techniques of sand roasting and baking are
gaining importance as cheap, effective, oil-free,healthier ways of
cooking. However, further studies are needed on micronutrient
availability and functional fooddevelopment for community
nutritional disorders. Also, the residual silica levels and
difficult working environmentmandates the development of
energy-efficient and high-output-orientated technologies such as
continuous,microwave, and fluidized bed roasters.
Keywords: Sand roasting, Sand baking, Antioxidant,
Digestibility, Snack, Nutrition
IntroductionIn terms of health benefits, minimally processed
foods arebetter than the processed foods. Among the minimal
pro-cesses, sand roasting is a traditional, rapid food
processingmethod which utilizes dry heat for a shorter span of
time.In this high-temperature short-time treatment, the heat
en-ergy is transferred via conduction. The sand roasting causes
faster dehydration, characteristic thermal and chemical
re-actions, and reduction in water activity of the grains.
Duringroasting, the far infrared rays produced from the sand
pene-trate the grains and aid in breaking down of the starch,
pro-tein, and fats in the grains
(http://www.vmosa.com/health04_en.htm, 2019). It aids in
digestibility improvementby converting the micro and macronutrients
into more di-gestible form via rapid starch gelatinization,
simultaneousdrying of gelatinized starch, and denaturation of
proteins. Itresults in higher puffing index, enhanced crispiness
and vol-ume, and improved texture. It also enhances the
color,aroma, flavor, shelf life, and consumer acceptance and
re-duces the bulk density and antinutrients present in cereals
© The Author(s). 2019 Open Access This article is distributed
under the terms of the Creative Commons Attribution
4.0International License
(http://creativecommons.org/licenses/by/4.0/), which permits
unrestricted use, distribution, andreproduction in any medium,
provided you give appropriate credit to the original author(s) and
the source, provide a link tothe Creative Commons license, and
indicate if changes were made.
Correspondence: [email protected] Centre for
Compositional Characterisation of Materials (NCCCM),Bhabha Atomic
Research Centre (BARC), ECIL PO, Hyderabad, Telangana500062,
India2Homi Bhabha National Institute (HBNI), Anushaktinagar, Mumbai
400094,India
Bulletin of the NationalResearch Centre
Kora Bulletin of the National Research Centre (2019) 43:158
https://doi.org/10.1186/s42269-019-0199-2
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and legumes (Jogihalli et al. 2017a; Sharma and Gujral2011). The
important cereals and legumes which are con-sumed in roasted form
after sand roasting are rice, maize,sorghum, wheat, barley, oats,
groundnut, black gram, bengalgram, chickpea, peas, and cowpea. The
roasting dependsupon on the sand temperature, temperature profile,
androasting time. They are usually roasted at a varyingtemperature
of 150–350 °C using sand as a heating medium,in small, medium, and
industrial pan roasters in a batchmode which is practiced in
villages and cottage industries ofIndia. The roasting process
affects the nutritional, antioxi-dant, sensory, and functional
properties of the products.The demand for value-added products such
as roasted ce-reals and grains is increasing, as it is a cheap,
effective, oil-free, healthy way of cooking (Jogihalli et al.
2017a; Singhet al. 2018).In the present review, the application of
sand roasting in
the production of value-added products from rice such aspopped,
puffed, and flaked rice; other popped and roastedcereals and
millets such as barley and oats; maize, sor-ghum, pearl millet, and
finger millet; and roasted legumessuch as groundnut, chickpea, pea,
cowpea is detailed. Inaddition, the importance of sand roasting in
terms of graincharacteristics, nutritional, antioxidant, sensory,
and func-tional properties of the products is highlighted. In
additionto vegetable and meat roasting, the application of
sandroasting as a pretreatment process in various nut
decorti-cation is covered. The applications of sand bath in
bakingof cakes, vegetables, meat, fish, eggs, and starchy tubersare
mentioned.
Sand roasting of cerealsThe cereals belong to the family
Graminaceae andinclude rice, wheat, maize, barley, oat, and rye.
Theyare the important carbohydrate resources, in additionto
minerals, dietary fiber, and bioactive compounds.The different
methods such as conventional dryheating, sand roasting, hot-air
popping, gun puffing,microwave heating are used for producing
value-added cereals with distinctive aroma and taste (Mis-hra et
al. 2014).
Sand roasting of riceAmong the cereal crops, rice (Oryza sativa)
occupiesa key position as a major cereal crop and staple foodin
human nutrition due to its texture, taste, and nu-tritional
qualities (Mir et al. 2016). There are vastnumber of paddy
varieties grown in different states ofIndia which are suited for
raw milling, parboiling, andvalue-added rice products. In India,
around 10% ofthe production (14.5 million tons) is used for
makingvalue-added rice products such as popped, puffed,and flaked
rice (Chitra et al. 2010).
Popped riceIt is known as pelalu, khoi, etc. in various Indian
languages.It is a traditional value-added product with high cold
waterswelling capacity originated from raw paddy; arising fromhigh
starch gelatinization and low retrogradation (Fig. 1a).It is
prepared directly by high-temperature short-time treat-ment from
the moisture-adjusted raw paddy (12–14%) bysand roasting in a pan
at a temperature of 150–250 °C for25–45 s. In comparison with other
value-added rice prod-ucts, popped rice production is less and
mostly used duringreligious ceremonies (Chitra et al. 2010;
Murugesan andBhattacharya 1989).
Puffed riceIt is known as maramaralu, murmura, murra, muri,puri,
borugulu, mandakki, kallepuri, etc. in various In-dian languages.
It is one of the popular, common, oldestminimally processed food
items especially used as snack,ready to eat breakfast cereal,
infant food, etc. in India. Itis also distributed as prasadam to
devotees in templesand gurudwaras. It is mostly produced in home or
cot-tage industries by skilled artisans using the cheaply
avail-able local material, sand as a heat transfer medium forthe
uniform distribution of temperature among thegrains. In different
regions of India, it is traditionallymade from the pregelatinized,
milled, parboiled rice byheating at a high temperature for a
shorter time in a hotsand bath and quickly stirring in large,
shallow iron orclay frying pans (Fig. 1b). The traditional fire
woodburning earthen stove known as bhatti and the locally
Fig. 1 Photographs of a popped rice, b puffed rice, and c flaked
rice
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available, cheaper fire wood from sarkar tumma (Proso-pis
juliflora), wood shavings ,and crop residues such asstraws of
cotton, chili, and agro-industrial residues, in-cluding rice husk,
bagasse, groundnut shell, coconutshell, and coir pith are employed
(Kumar and Prasad,2013; Mir et al. 2016).There are different steps
involved in the puffed rice-
making process by sand roasting. First one is the selec-tion of
paddy variety that is suitable for puffing andavailable at a
cheaper price. Generally, coarse, short,thick-grained,
non-glutinous, medium amylose rice isused for puffing. The second
step is the parboiling thepaddy, which is done by soaking,
steaming, and dryingthe grains. The paddy is soaked in water at
roomtemperature for 4–5 days or in preheated water at 70–80 °C for
6–8 h; water is drained and steamed at 100 °Cin an open boiler or
in an autoclave under pressure for10–20min. Then, the paddy is
dried and milled. Theparboiling is a hydrothermal process in which
the starchgranules are gelatinized and retrograded that helps
ingrain expansion during puffing. The milled, parboiledrice is
preconditioned by soaking in salt water to obtainmoisture content
of 14–20% and roasted in a sand bathat 220–285 °C for 10–25 s
within which the grains willpuff up. The grains expand nearly 8
times, becomehighly porous, lighter, and crispy, as a result of
physical,morphological, conformational, and structural changesin
the grains. The high temperature during roastingcauses rapid water
evaporation, creates many void spacesdue to the high pressure
exerted by the steam formedinside the grains, and forces the
retrograded starch toexpand. The puffed rice is quickly separated
from thesand using a metallic strainer and cooled to
roomtemperature. The collected puffed rice is packed in bagsand
marketed. The same method with variations is prac-ticed in India
for many decades and still it is continued.The critical parameters
involved in the entire processare the amylose content of the
parboiled rice, moisturecontent in the grains (10–20%), heating
medium (sand),maintenance of required puffing temperature (220–285
°C) and roasting time (8–25 sec) (Ashwini et al.2016; Chinnaswamy
and R. Bhattacharya 2006; Kumarand Prasad, 2013; Mir et al. 2016).
The puffing processdiffers from the popping in which controlled
expansionof the kernel is done during the vapor pressure escapefrom
the grains’ micropores because of high pressure orthermal gradient
(Mishra et al. 2014).
Flaked riceIt is also known as rice flakes, parched rice,
flattened rice,and beaten rice in English and atukulu, avalakki,
aval,poha, chura, chira, chiwada, etc. in various Indian
lan-guages. It is one of the oldest traditional rice productwhich
is consumed as a cereal breakfast and sweet or salty
snack either by toasting, roasting, frying, spicing, or soak-ing
in water, milk, and seasoning with vegetables andspices in India.
It is a flattened, carbohydrate rich, edible,precooked, rice
product produced by soaking the paddy,sand roasting, and flattening
(Fig. 1c). The paddy is soft-ened by soaking in water for 2-3 days
at room temperatureor in warm water (40-50 °C) for 18–24 h to
obtain a mois-ture level of 30%. The water drained, soaked paddy
issand-roasted in a shallow iron pan or earthen vessel at150–180 °C
for 28–50 s to reduce the moisture content.The hot paddy with a
moisture content of 17–20% is flat-tened subsequently into flakes
in an edge runner or rollerflaker. The roasted grains pass
repeatedly between theroller and pan edge of the edge runner,
leading to thedehusking of the kernels and formation of thin,
papery,white rice flakes (Chitra et al. 2010; Dutta 2014; Kumarand
Prasad, 2017; Mujoo and Ali 1998).The sand roasting method is also
employed for dry-
ing high moisture paddy harvested during the mon-soon. The high
moisture content (18–23%) is reducedto 5–10% by roasting in a
commercial sand roaster at95–155 °C for 1–1.5 min, without
affecting the millingcharacteristics (Srinivas et al. 1981).A study
carried out on brown rice puffing indicated no
loss of minerals, but a slight increase in essential trace
ele-ments such as potassium, magnesium, manganese, andphosphorous
after puffing in comparison with raw rice (Miret al. 2016). In a
study on content and digestibility of starchin sand-roasted
products; in comparison with raw rice, thestarch content was
decreased, attributed to resistant starchformation and adhering
bran layers. The resistant starch for-mation during the sand
roasting of popped rice may find ap-plications in diabetic food
preparation. While the in vitrodigestibility of the popped, puffed,
and flaked rice was in-creased when compared with raw rice, which
is accountedfrom amylopectin structure damage. Also, the increased
di-gestibility of the sand-roasted products suits children
andelderly people with a poor state of digestibility (Chitra et
al.2010; Dutta 2014; Dutta et al. 2016). In another study onstarch
susceptibility to enzymatic hydrolysis; the digestibilityof the
flaked rice was higher when compared with raw rice,attributed to
gelatinization and mechanical damage of starchduring sand roasting
(Mujoo and Ali 1998). Another studyindicated an enhancement in
protein solubility, upon sandroasting of soaked paddy at 175–250 °C
(Mujoo et al. 1998).In addition, the flaked rice is known to
contain higheramounts of dietary fiber, minerals, and oryzanol than
themilled raw rice. The nutritionally important, resistant
starchformed in puffed and flaked rice is unaffected during
diges-tion and absorption in the small intestine. It acts as a
dietaryfiber and responsible for controlling coronary heart
diseasesand diabetes via lowering the blood cholesterol and
glycemicindex, respectively. Also, it functions as prebiotic
nutrientfood to gut microflora, maintains the gut health and
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prevents the risk of colon cancer and other celiac diseases.In
addition to serving as a low-cost, conventional, nutritious,and
easily available food to masses, the gluten-free, roastedrice
products are alternative to wheat products for patientssuffering
with celiac diseases (Kumar and Prasad, 2013;Kumar and Prasad,
2017).
Sand roasting of maizePopcorn is the most important, popular
commercialsnack produced worldwide from corn (Fig. 2a). It
isavailable in small packs, coated with various ingredientssuch as
hydrogenated oil, sugar syrup, salt, β-carotene,favors, etc. for
improving the sensory quality. There arevarious corn-popping
methods are available includingconventional sand roasting, gun
popping, hot-air pop-ping, and microwave popping. Among which, the
micro-wave and pressure cooker popping are the most popularmethods
at households due to energy-efficiency andshort time. The popping
of maize depends on corn var-iety; kernel size, shape, and density;
pericarp thickness;moisture content (11-16%); popping temperature;
andpopping method. The large kernels expand less than thesmaller,
shorter. and broader kernels due to high levelsof soft endosperm.
During popping, the pericarps of thekernels act as pressure vessels
and popping happens atrespective temperature and pressure of 177 °C
and 135psi inside the kernels. The super-heated water
vaporizes,expands the starch granules into a thin film
viagelatinization and generates large voids, leading to
theproduction of popped corn. It is important to note thatduring
popping, most of the seed microflora aredestroyed and the produced
popcorn is sterile (Mishraet al. 2014).
In the preparation of ready to eat foods such as corngrit, the
preconditioned corn kernels with a moisturelevel of 20% are sand
roasted at 191 °C for 104 s (Kumaret al. 2018). Also, the
sand-roasted corn on the cobknown as bhutta is one of the most
common, favorite,affordable, healthy street side snack in India,
along withcharcoal roasted corn on the cob. Also, it is a
general
practice to roast the corn kernels alone in hot sand(Kamal
2012).
Sand roasting of barleyBarley scientifically known as Hordeum
vulgare is one ofthe ancient, important cereal crops and ranked
fifth interms of world production. The whole barley grains
areroasted at 250–300 °C for 2min in hot sand bath and huskis
removed. The roasted grains are milled to flour knownas sattu,
which is widely consumed as a snack in India. Itis abundant in
soluble and insoluble fibers, β-glucans,phenolics, and antioxidants
such as pro-anthocyanidins,flavonols, flavones, flavanones,
quinines, chalcones, andbenzoic and cinnamic acid derivatives. The
β-glucans playan important role as soluble, dietary fiber in
relieving con-stipation. It is also involved in the reduction of
dietarycholesterol absorption and glycemic index and preventionof
diet related disorders including diabetes and coronaryheart
diseases. It is widely used in malting, brewing, bak-ing and the
production of feed and alcohol. The abun-dance of antioxidants in
barley aids in food preservationvia lipid peroxidation inhibition
(Rashid et al. 2015;Sharma and Gujral 2011; Sharma et al. 2011).The
effect of sand roasting and microwave cooking on
antioxidant activity was investigated in a previous com-parative
study. The hulled seeds of different barley culti-vars were roasted
at 280 °C for 20 s in a traditionalroaster made up of an iron pan
with sand. It was re-ported that the sand-roasted barley showed
higher anti-oxidant and metal chelating activities, reducing
powerand non-enzymatic browning in comparison with micro-wave
cooked barley. Also, the sand-roasted barley exhib-ited higher
retention of total phenolic and flavonoidcontent in comparison with
microwave cooking (Sharmaand Gujral 2011). The roasted barley at
identical condi-tions showed higher water absorption, water
solubilityindex, and oil absorption capacity which is accountedfor
porous structure formation in the endosperm andhigher content of
cooked and damaged starch (Sharmaet al. 2011). In a similar study,
the effect of sand roastingon antioxidant and anticancer activity
of barley was
Fig. 2 Photographs of a popped maize, b popped sorghum, and c
popped pearl millet
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evaluated. It was observed that the sand roasting at280 °C for 2
min caused considerable enhancement in 1-diphenyl-2-picrylhydrazyle
(DPPH) and hydroxyl radicalscavenging activities, reducing power
and cell prolifera-tion inhibition, when compared with uncooked
barley(Rashid et al. 2015).
Sand roasting of oats and wheatIn terms of world production,
oats (Avena sativa) standin the sixth position and it is cultivated
as a fodder cropin area of 1 lakh hectares of land in India. It is
recog-nized as a functional food due to the abundance of β-glucan,
antioxidants, soluble fiber, and minerals. Thephytochemical
β-glucan is known to reduce the serumcholesterol and postprandial
blood glucose levels. In astudy carried out on ten different oat
cultivars, the im-pact of sand roasting on β-glucan extractability
and anti-oxidant activity was studied. The hulled oats were
sandroasted in a traditional sand roaster at 280 °C for 15 s. Itwas
found that the sand roasting significantly increasedβ-glucan
availability, reducing power, DPPH radicalscavenging, and metal
chelating activities. The increasein β-glucan extractability is
accounted to its release fromthe cellulose and other non-cellulosic
cell wall polysac-charides of the grains by thermal effect of
roasting (Guj-ral et al. 2011). In another study, the effect of
sandroasting on various parameters of wheat (Triticum aesti-vum L.)
was studied. The wheat was roasted at 300 °Cfor 25–30 s by
traditional method of pan roasting insand. It was noted that sand
roasting caused a consider-able decrease in moisture content, bulk
density, andchroma values and an increase in crispiness and
porosityin comparison with the raw wheat (Murthy et al. 2008).
Sand roasting of milletsIn terms of nutritional values, the
millets are comparableor even better than the staple cereals such
as rice andwheat. They are the cost-effective sources of
protein,minerals, and vitamins for poor people. The millets arethe
main food and fodder crops in semi-arid regions,characterized by
small grains compared to maize. How-ever, due to antinutrient
presence and poor protein andcarbohydrate digestibility, processing
of millets withtechniques such as dry conduction heating or malting
ismandatory (Choudhury et al. 2011). The whole grains ofmillets
such as sorghum, pearl millet, and finger milletare popped by dry
heating on sand baths, which is acommon practice in villages
(Nations 1995). The pop-ping under high temperature for a short
duration time isa process of simultaneous starch gelatinization and
ex-pansion that results in super-heated vapor productioninside the
grains, sudden endosperm expansion andbreaking out of outer skin
(Mishra et al. 2014).
The popped sorghum is a ready to eat snack,
producedtraditionally in a batch process by manual sand roastingin
cottage industries and villages of India. It is producedfrom the
grains with a moisture content of 16–80% bysand roasting in a
wide-mouth concave pan at 240 °C for1 min by continuously agitating
with iron ladle (Fig. 2b).The popped grains expand nearly 8 times
and are sepa-rated from the sand with a perforated pan. As it is
pro-duced from the whole grains, it is bestowed with all
thenutrients of native sorghum (Benhur et al. 2016; Nations1995).
The high popping yield and greater volume ex-pansion of millets
depend upon the variety, grain charac-teristics such as size,
weight, bulk density, hardness,moisture, protein and amylose
content, endosperm type,and popping method (Mishra et al. 2014).
When com-pared to boiling, popping is an energy-efficient and
nu-tritionally desirable process. It utilizes less fuel
andmarginally hydrolyses the proteins and vitamins, inaddition to
improvement in flavor. In Central India, it ismostly consumed by
school going children as a snackand drinks, derived from the
pounded, popped sorghumflour. The popped sorghum is used in weaning
food for-mulations and in the form of flour and laddu during
fes-tivals (Mishra et al. 2014). The whole, sorghum seedheads known
as panicles harvested during the doughstage are roasted in hot sand
and thus obtained soft,sweet seeds are used as a snack. These
sugary endo-sperm varieties with 30% glycogen are found in
theMaharashtra state of India (Council; et al. 1996).In a study
carried out on pearl millet (Pennisetum
glaucum), the effect of sand roasting on physical
charac-terstics, texural properties, and sensory attributes
inmaking sattu was studied (Fig. 2c). Sattu in drink formis
considered as the best breakfast food during summerseasons due to
its cooling effect and good digestibility. Itis prepared from the
roasted cereals, legumes, or com-bination of both with added
flavoring agents. It wasfound that the sand roasting at 180 °C for
1 min is opti-mal for making sattu (Mridula et al. 2008). For the
fin-ger millet (Elusine coracana), the optimal poppingconditions
were found to be 19% moisture and sandroasting at 270 °C (Malleshi
and Desikachar 1981). Inaddition to finger millet, the other minor
millets such asfoxtail millet, barnyard millet and proso millets
werepopped with roasting and highest popping yield and ex-pansion
volume was obtained with proso millet (Srivas-tava and Batra 1998).
In another study carried out onminor millets including foxtail
millet, barnyard millet,kodo millet, proso millet, and little
millet; the highestpopping and expansion ratios were obtained with
kodomillet followed by little millet (Mishra et al. 2014).In a
study carried out on carbohydrate and protein di-
gestibility of foxtail millet (Setaria italica), the two
pro-cessing techniques such as sand roasting and malting
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were compared. The grains with 10% moisture poppedby sand
roasted at 230 °C for 15 s showed higher carbo-hydrate and protein
digestibility in comparison withmalted and raw grains. It is
attributed to starch granulerelease form protein matrix and reduced
antinutrientsleading to enhanced amenability to enzymatic
digestion.Thus, the sand-roasted millets could be utilized in
thepreparation of cost-effective, dietary formulations forchildren
and geriatrics (Choudhury et al. 2011).
Sand roasting of legumesThe seeds of various leguminous plants
such as ground-nut, chickpea, pea, cowpea, red gram, and soybean
aresand roasted for the preparation of snacks and othervalue-added
food products in India.
Sand roasting of groundnut fruits and seed kernelsThe groundnut
(Arachis hypogea) seeds are the plantsource of carbohydrates,
dietary protein, essential min-erals, vitamins, and healthy fats in
sufficient quantities.It is ranked at third position in abundantly
cultivated oil-seeds in the world. In India, it is grown in the
rain-fedareas of Gujarat, Andhra Pradesh, and Tamil Nadustates
(Nirmale et al. 2017). Traditionally, the fruits andseed kernels
are roasted in small, open-sand bath panroasters (Fig. 3a). The
roasting is critical in determiningthe flavor, texture, and
nutritional values of the kernels.The sand roasting is one of the
oldest cooking tech-niques used by the street side food vendors and
villagersof India for obtaining crunchy, crispy, crackling,
androasted peanuts (www.myKottayam.com 2017). For thepurpose of
roasting groundnut fruits and seed kernels, a
clay pot specially designed for sand roasting known asmangalam
is used in the villages of Andhra Pradeshstate. It is made from an
old or unused or leaky clay potin which a hole is made on one side
to insert a woodenladle for mixing during roasting (Fig. 3b)
(Wikipedia2019). The dry roasted peanuts provide sufficient
quan-tities of mono-unsaturated fatty acids in diet and reducelow
density lipoprotein cholesterol level in the blood,there by
prevents the chance of coronary artery diseases(Fig. 3c). Also, dry
roasting reduces the aflatoxin levelsin the groundnuts. Further,
roasting releases polyphenolssuch as p-coumaric acid and
hydroxybenzoic acid,known antioxidants which limit the carcinogenic
nitro-samine formation in stomach and decrease stomach can-cer risk
(Chikelu et al. 2015).Many food industries use the roasted peanuts
for
making various food products, which mandates theuse of peanut
processing machines for peeling. For ef-fective peeling, the
peanuts should be sand roastedand the sand temperature is kept in
the range of150–160 °C for 45–60 s (Nirmale et al. 2017). In
thepreparation of chikki, which is a jaggery-based, sweetsnack; the
groundnuts which are low in fat levels andless prone to rancidity
upon storage are selected. Forthis, the kernels are medium roasted
in a sand bathat 120–125 °C and used during the sweet
preparation(Manay and M. 2008). The vitamin E is an
importantmicronutrient derived from the plant oils and acts asan
antioxidant, prevents essential fatty acids oxidationin the body,
and fights against coronary heart diseasesand cancer. The vegetable
oil derived from groundnutis a rich source of vitamin E. In an
earlier report, the
Fig. 3 Photographs of sand roasting of peanut fruits in a an
open iron pan; b a traditional, designed pot mangalam; and c
sand-roasted peanuts
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vitamin E content of groundnut which was tradition-ally sand
roasted in an open aluminum pot for 30min was studied. It was found
that the vitamin Elevel was higher in the roasted groundnuts than
inthe raw groundnuts (Ejoh and Ketiku 2013).
Sand roasting of chickpea, cowpea, pea, black gram, andkidney
beansThe chickpea (Cicer arietinum) is one of the main leg-ume
crops in Indian sub-continent and stands as an im-portant resource
for proteins and carbohydrates. Interms of protein quality, it is
superior to other legumessuch as red, black, and green gram. The
seeds are classi-fied as desi (Indian origin) and kabuli
(Mediterraneanand Middle Eastern origin) types based on seed
colorand geographic distribution (Kaur et al. 2005).In India, the
roasted chickpea is a popular, traditional
snack consumed daily due the abundance of
carbohydrates,proteins, essential amino acids, minerals, and
dietary fiber(Fig. 4a). It is used for the preparation of sattu
(roastedgrain powder), fortified extruded foods, drinks, sweets,
etc.(Fig. 4b). For the development of value-added products,
thechickpeas are roasted at 150–350 °C using conduction,
con-vection, and radiation modes of heat. In a contemporarystudy,
the effect of sand roasting on physico-functional andantioxidant
properties of chickpea was evaluated. The opti-mally sand-roasted
chickpea grains at 180 °C for 5minshowed an increase in the surface
area and a decrease inthe bulk density. Also, the sand roasting
caused an increasein water and oil absorption capacities and water
absorptionindex. In the process of roasting, the grains are exposed
tohigher temperature for a shorter duration of time duringwhich the
imbibed water is transformed to vapor. The gen-erated steam within
the compact grain structure causesgrain puffing, leading to void
generation in the cellularmatrix, starchy endosperm expansion, and
enhancement insurface area. Subsequently, the increase in volume
and fas-ter removal of moisture causes a decrease in the bulk
dens-ity of the roasted grains. The sand roasting at a
moderatetemperature exhibited an increment in total phenolic
con-tent and DPPH activity, attributed to heat-induced,
extract-able phenolic release and formation of Maillard
reaction
products that occurs only above a temperature of 120 °C. Itis
worth noting that the sand roasting also bestows texture,flavor,
and aroma to the grains as a result of starchgelatinization;
formation of desirable acid aromatic com-pounds, esters and alkenes
during Maillard reaction; incre-ment in levels of nitro compounds,
melanoidins, biogenicamines, and lipid peroxidation products; and
alteration inthe composition of olefins, lipids, and alkenes
(Jogihalliet al. 2017a; Jogihalli et al. 2017b). It was found that
amongthe desi and kabuli varieties sand roasted at 190 °C for 5min,
the desi variety PDG-3 was suitable for roasting. It isdue to its
highest puffing capacity, puffing index, leastbreaking strength,
and percent hard-shelled grains (Kauret al. 2005).In another recent
study on chickpea, the optimum
sand roasting was recorded at 220 °C for 10 min forobtaining
higher puffing index, lower hardness, and rup-ture energy (Singh et
al. 2018). In a different study, theantioxidant properties of
chickpea seeds sand roasted at280 °C for 25 s were compared with
raw seeds. Theroasting treatment augmented the total phenolic
con-tent, reducing power, metal chelating, and
antioxidantactivities (Gujral et al. 2013). In another work, the
nutri-tional quality of the chickpea seeds roasted on a sandbath at
180 °C for 20 min was compared with pressurecooked and raw seeds.
The sand roasting treatmentretained most of the minerals including
sodium, potas-sium, magnesium, iron, and phosphorous; amino
acidsespecially lysine, leucine, valine, cysteine, and tyrosine;and
polyphenols present in the raw seeds when com-pared with pressure
cooking (Daur et al. 2008). In anearlier reported case on chickpea
and black gram (Vignamungo), the sand roasting treatment at 220 °C
for 5 mindid not show significant change in the fatty acid
com-position of the extracted oils (Liaquat et al. 2008).The
occurrence of antinutrients in legume seeds limits
their applications as food and feed, even though they arethe
basic sources of proteins, minerals, and vitamins.The
antinutritional factors include tannins, phytic acid,trypsin
inhibitors, and flatulence causing oligosaccha-rides. The tannins
limit the digestibility of proteins andcarbohydrates by the
inhibition of digestive enzymes.
Fig. 4 Photographs of a sand-roasted chickpeas; b spitted,
dehusked sand-roasted chickpeas; and c sand-roasted peas
Kora Bulletin of the National Research Centre (2019) 43:158 Page
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The phytic acid decreases the bioavailability of
essentialdietary minerals, proteins, and starch in humans bybinding
to them. On the other hand, the trypsin inhibi-tors reduce the
digestion and absorption of dietary pro-teins by severe inhibition
of the enzyme trypsin. In aprevious study carried out on the effect
of physical treat-ments on nutritional quality of legume seeds, the
con-centration of antinutrients was investigated. The cowpea(Vigna
sinensis L.), pea (Pisum sativum L.), and kidneybeans (Phaseolus
vulgaris L.) were roasted in a sand bathat 180 °C for 15 and 20min,
respectively (Fig. 4c). Theapplied sand roasting caused significant
decrease in tan-nin, phytic acid, trypsin inhibitor, and
oligosaccharidecontent in comparison with the raw seeds.
Especially,the sand roasting completely removed the of trypsin
in-hibitors (Khattab and Arntfield 2009). The essentialamino acid
content was also increased after sand roast-ing as compared with
raw seeds (Khattab et al. 2009). Inanother study on cowpea, the
sand roasting was foundto be superior in comparison with
microwaving in termsof puffing and sensory results (Kamble 2017).
Inaddition, the sand roasting technique is also employedfor
roasting peas, bengal gram, black gram, and soybean.
Sand roasting of other food itemsThe low carbohydrate sun flower
kernels which are abun-dant in unsaturated fatty acids, proteins,
minerals, and vi-tamins are also sand roasted for obtaining tasty,
aromatic,crunchy, and crispy-textured snacks (Mosayebi et al.2018).
Also, the chestnuts and coffee beans are sandroasted for the
characteristic aroma (DeAangelis, 2015).The technique is also used
for oil-free roasting of starch-based fryums known as vadiyalu and
appadalu made upof rice and black gram flour, respectively (Fig.
5a).The sand roasting is also employed for making
anardana. In Himachal Pradesh state of India, theanardana
production is a household activity. It isprepared from the seeds of
wild, culled, or highlyacidic pomegranate fruit varieties by sand
roasting foreasier separation of tightly adhered seeds. The
dehy-drated seeds are acidic, abundant in vitamin C andminerals,
and extensively used in culinary prepara-tions as a substitute for
tamarind and mango slices;
for garnishing ice cream, chutney, fruit salad, and panmasala;
and preparation of digestive and other ayur-vedic medicines
(Parashar et al. 2009).
Other applications of sand roastingThe sand roasting is one of
the simplest, convenient,and oldest industrial techniques employed
for seed coatremoval from tamarind seeds. The seeds are roasted
inhot sand bath at 100–250 °C for 2–3 min for looseningthe testa
from the seed kernel. The loosened seed coat isremoved by rubbing
in a decorticator followed by aspir-ation and separation (Fig.
5b–d). The kernels rich instarch are pulverized into tamarind
kernel powder(TKP), a value-added product. The roasting
temperatureand time determines the subsequent steps such as
dehul-ling and grinding of the kernels and the color of theground
kernel powder. The TKP is extensively used as asizing, binding,
film forming, coating, conditioning, gel-ling, thickening,
stabilizing, bulking, dehydrating, glaz-ing, drug delivery agent,
adhesive, emulsifier, disperser,and food additive in textile, jute,
plywood, paper, leather,printing, food, and pharmaceutical
industries (Bharadwajet al. 2007; Bhattacharya 2014; Thombare et
al. 2014).
Generally, the processing of nutmeg nuts into kernelsis a
tedious, time-consuming, and drudgery operation.It involves
decortication, separation, and grading due tothe lack of efficient
mechanical equipment. Hence, vari-ous preshelling treatments which
affect the physicaland mechanical properties of nutmeg nuts before
de-cortication was investigated. The sand roasting at 60 °Cfor 20
min is used as a pretreatment method before thedecortication of
nutmeg nuts (Said et al. 2013). Thesand medium is also used for
decortication of thecashew nuts (Anacardium occidentale L.) and
roastingof the kernels (Emelike and Ebere 2015). In comparisonwith
cold, water, and steam treatments which are im-posed for softening
the shells; the sand roasting of Cud-dapah almond (Buchanania
axillaris) fruits at 60 °C for20 min gave a higher kernel recovery
by the decorti-cator. It is also employed as preconditioning
processfor aiding in subsequent decortication of various
pulses(Jadhav Vinayak, 2010).
Fig. 5 Photographs of a sand-roasted fryums, vadiyalu and b
sand-roasted tamarind seeds, c separated seed testam and d
decorticatedseed kernels
Kora Bulletin of the National Research Centre (2019) 43:158 Page
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Sand baking of vegetables, eggs, meat, and cakeSand baking is a
method of slow cooking during whichthe food is exposed to dry heat
for longer times, employ-ing sand as the heat transfer medium.
During baking,the heat is steadily transferred from the surface to
thecenter results in formation of baked food with dry crustand a
soft center. It is used as one of the slow cookingmethods for meat
and vegetables in coastal areas such asGoa, where the sea sand is
abundant. The marinatedvegetables or meal wrapped in aluminum foil
and cov-ered with flat dough, resembling a chapati are placed ina
pan or tray filled with sand and slow cooked. The bak-ing time
varies based on the type of food, i.e., 30, 40,and 120 min for
vegetables, fish, and meat, respectively.This slow cooking method
prevents the ingredients fromburning, retains the flavor, and,
devoid of oil or less useof oil, makes it a tasty and healthier
cooking. It is prac-ticed as a fun group activity for family
members andfriends during camp nights. In villages, it is common
tobake meat and fish wrapped and tied in banana leaf inhot sand.
Also, it is a traditional practice to bake theclay-wrapped eggs in
hot sand by the agricultural laborin fields. Similarly, starchy
tubers such as potatoes, sweetpotatoes, taro, tapioca, and yams are
also sand baked.Sometimes corn ears are also baked in hot sand for
5–6h (Das 2017; Nair 2018). The cake baking with hot sandis an
age-old, traditional practice in many countries andnow also it is
considered as a viable alternative to micro-wave baking (Fig.
6).
ConclusionsThe sand roasting technique is used extensively in
Indiaby street food vendors, villagers, and cottage industriesfor
the production of various ready to eat food productsfrom different
cereals, millets, and legumes. The processnot only enhances the
sensory characteristics of theproducts such as aroma, texture,
crispiness, volume, etc.but also improves the nutritional and
antioxidant values.
They include reduction in antinutritional factors, de-struction
of seed microflora, enhancement in carbohy-drate and protein
digestibility; β-glucan extractability,dietary fiber, vitamin E,
minerals, shelf life, consumer ac-ceptance, and antioxidant levels.
In terms of value-addedhealth products, the sand-roasted products
act as pre-biotic dietary fiber and serves as an alternative
topolished or refined grains for the consumers. Thus, thesimplest,
inexpensive, traditional sand roasting methodof dry heat
application is employed for making pre-cooked ready to eat weaning
foods and preparation ofcost-effective dietary formulations for
children and geri-atrics. The technique is also used for roasting
beans,fryums, and as a pretreatment process for
commercialproduction of TKP and decortication of nuts and
pulses.Also, the sand baking method is widely used for bakingcakes,
vegetables, meat, fish, eggs, and starchy tubers.However, further
studies are needed on micronutrientavailability and development of
functional foods forcommunity nutritional disorders.The limitations
of the sand roasting technique are lack
of temperature control, uneven temperature distributionand sand
contamination in the final products (Sharma andGujral 2011). The
sand roasting method is energy ineffi-cient, tedious, manual in
operation involving continuoushand stirring, sometimes unhygienic,
and limited by lowoutput. The workers are prone to direct influence
of heat,flame, and smoke originated from the commonly usedfuels
such as crop and agro-industrial residues, wood,charcoal, kerosene,
and gas (Chikelu et al. 2015; Murthyet al. 2008). Thus, the current
traditional and industrialsand roasting method necessitates the
development an al-ternate technology for production of value-added
cerealand legume food products which is low-cost, energy-efficient,
effective, high-output-orientated with no expos-ure of the food
products to impurities. For example, con-tinuous, microwave, and
fluidized bed roasters save cost,reduces the manual labor, enhances
productivity, and
Fig. 6 Photographs of common, household baking vessel a before,
b during, and c after sand baking of the cake
Kora Bulletin of the National Research Centre (2019) 43:158 Page
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maintains uniformity in roasted products. In addition toconsumer
satisfaction, it also provides temperature rangeoptimization, even
heat distribution within the heatingchamber and food grains and
applicability to wide rangeof materials (Jogihalli et al.
2017a).
AcknowledgementThe author would like to thank Dr. Athyala
Christian Sahayam, Head, BulkAnalysis Section (BAS), and Dr. Sunil
Jai Kumar, Head, NCCCM/BARC, for theirconstant encouragement and
support throughout the study.
Authors’ contributionsThe author alone was involved in data
collection, compilation, writing, andinterpretation during the
manuscript preparation. The author read andapproved the final
manuscript.
FundingNo funding source to declare.
Availability of data and materialsNot applicable
Ethics approval and consent to participateNot applicable
Consent for publicationNot applicable
Competing interestsThe author declares that she has no competing
interests.
Received: 1 August 2019 Accepted: 21 September 2019
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AbstractBackgroundResultsConclusions
IntroductionSand roasting of cerealsSand roasting of ricePopped
ricePuffed riceFlaked riceSand roasting of maizeSand roasting of
barleySand roasting of oats and wheat
Sand roasting of milletsSand roasting of legumesSand roasting of
groundnut fruits and seed kernelsSand roasting of chickpea, cowpea,
pea, black gram, and kidney beans
Sand roasting of other food itemsOther applications of sand
roastingSand baking of vegetables, eggs, meat, and
cakeConclusionsAcknowledgementAuthors’
contributionsFundingAvailability of data and materialsEthics
approval and consent to participateConsent for publicationCompeting
interestsReferencesPublisher’s Note